he limb is more marked than in the sub-coracoid
variety. The treatment is the same as for sub-coracoid dislocation.

#Sub-glenoid dislocation# (Fig. 17) is less frequently met with than
the sub-coracoid variety, and almost always results from forcible
abduction of the arm. The head of the humerus passes out through a
small rent in the lower and medial portion of the capsule, and rests
against the anterior edge of the triangular surface immediately below
the glenoid cavity, supported behind by the long head of the triceps,
and in front by the subscapularis muscle. It is readily felt in the
axilla. All the tendons in relation to the upper end of the humerus
are stretched or torn, and the great tuberosity is not infrequently
avulsed. There is sometimes bruising of the axillary nerve.

The projection of the acromion, the flattening of the deltoid, the
increased depth of the axillary fold, and the abduction of the elbow
are well marked; the arm is slightly lengthened, rotated out, and
carried forward. It is reduced by the hyper-abduction method (p. 60).

#Sub-spinous Dislocation.#--Backward dislocation is usually termed
sub-spinous, although in a considerable proportion of cases the head
of the humerus does not pass beyond the root of the acromion process
(_sub-acromial_) (Fig. 17). This dislocation is usually produced by a
fall on the elbow, the arm being at the moment adducted and rotated
medially, so that the head of the humerus is pressed backwards and
laterally against the capsule, which ruptures posteriorly. All the
muscles attached to the upper end of the humerus are liable to be
torn, and the tuberosities are frequently avulsed. The long tendon of
the biceps may slip from its position between the tuberosities, and
prevent reduction or favour re-dislocation, necessitating an open
operation.

In the milder cases the _clinical features_ are not always well
marked, and on account of the swelling this dislocation is apt to be
overlooked. In addition to the ordinary symptoms, the shoulder is
broadened, there is a marked hollow in front in which the coracoid
projects, and the arm is held close to the side with the elbow
directed forward. The head of the bone may be seen and felt in its
abnormal position below the spine of the scapula.

Reduction can usually be effected by making traction on the arm with
medial rotation, and pressing the head forward into position, while
counter-pressure is made upon the acromion.

_P